1. Field of the Invention
The present invention relates to a waveguide and a microwave ion source.
2. Description of the Related Art
Conventionally, a waveguide has widely been used to guide an electromagnetic wave such as a microwave. As such a waveguide, a waveguide has generally been known, in which a core material made of a nonconductor is inserted into a metal tube molded in a cylindrical shape, and an inner peripheral surface of the metal tube and an outer peripheral surface of the core material are bonded to each other. A waveguide has also been known, in which an outer peripheral surface of a nonconductor is covered with a thin film made of a metal such as aluminum or copper (e.g., see Japanese Patent Laid-Open SHO 62 (1987)-278802).
However, there is room for improvement in all the conventional waveguides when they are applied to microwave ion sources or the like.
That is, in the case of the waveguide in which the core material is inserted into the metal tube, it is difficult to completely bond the inner peripheral surface of the metal tube and the outer peripheral surface of the core material to each other, and a very small gap is frequently generated between the surfaces. If such a gap is generated between the waveguide and the core material, a conduction loss is increased due to reflection of an electromagnetic wave in the gap. Additionally, for example, as an atmospheric temperature of the microwave ion source rises even to several hundred ° C., the metal tube and the core material may shift from each other due to a difference in coefficients of thermal expansion to generate a gap. Further, the difference in coefficients of thermal expansion between the metal tube and the core material may cause physical deterioration of the waveguide.
On the other hand, the waveguide described in Japanese Patent Laid-Open SHO 62 (1987)-278802 is designed to solve designing and processing problems of the waveguide in which the core material is inserted into the metal tube. However, it is still insufficient for practical application as a phenomenon of peeling-off of the metal thin film from the waveguide main body or a phenomenon of deterioration of the thin film itself tends to occur.